dbms數據庫管理系統

DBMS數據庫語言 (DBMS Database languages )

Database languages are the languages that provide the facility to specify the database schema and to express database queries and updates. They are further divided into four categories but all are purposed to provide the facilities in their specific ways and the most widely used database language is SQL language.

數據庫語言是提供用于指定數據庫架構以及表達數據庫查詢和更新的工具的語言。 它們被進一步分為四類，但是所有的目的都是以其特定的方式提供這些功能，并且使用最廣泛的數據庫語言是SQL語言。

Let us understand the basics of the Database Languages, what's their task are and how they perform it.

讓我們了解數據庫語言的基礎知識，它們的任務是什么以及它們如何執行。

1)數據定義語言 (1) Data Definition Language)

A Data Definition Language is a special kind of language that used to specify the database schema by the set of definitions. DDL is also purposed to specify the additional properties of the data.

數據定義語言是一種特殊的語言，用于通過定義集指定數據庫架構。 DDL還旨在指定數據的其他屬性。

There is a special type of DDL named as Data Storage and Definition language that specify the storage structure and access methods used by the database system. The hidden details for the implementation of the database schemas from the users are defined by these statements. Also, the data values that are stored in the database are required to satisfy certain consistency constraints.

有一種特殊的DDL類型，稱為數據存儲和定義語言 ，用于指定數據庫系統使用的存儲結構和訪問方法。 這些語句定義了用戶對數據庫模式實施的隱藏詳細信息。 而且，需要存儲在數據庫中的數據值滿足某些一致性約束 。

For e.g. – A university is required to fulfill the criteria of the marks of the students never be negative. DDL provides facilities to specify such type of constraints. Every time the database gets updated, these constraints are being checked by the database system. These constraints can refer to the arbitrary predicate for the database. But these arbitrary predicates are costly for the tests. Therefore, in that case, integrity constraints are implemented by the database systems so that these constraints can be tested with less overhead and more accuracy.

例如 -要求一所大學達到學生分數標準，決不能是負面的。 DDL提供了指定這種約束類型的工具。 每次更新數據庫時，數據庫系統都會檢查這些約束。 這些約束可以引用數據庫的任意謂詞。 但是這些任意謂詞對于測試而言是昂貴的。 因此，在那種情況下，完整性約束由數據庫系統實現，以便可以用更少的開銷和更高的準確性來測試這些約束。

• Domain Constraints

  域約束

  These are the most basic form of integrity constraint. In the database, they can be easily tested by the system every time a new data item is entered. Domain needs to be related to every attribute such as integer, character, date/time types. These attributes related to domain further acts as constraints on the values associated with it.

  這些是完整性約束的最基本形式。 在數據庫中，每次輸入新數據項時，系統都可以輕松測試它們。 域需要與每個屬性相關，例如整數，字符，日期/時間類型。 與領域相關的這些屬性進一步充當對與其相關聯的值的約束。

• Referential Integrity

  參照完整性

  Referential integrity means the value that is in the one relation must also appear in a certain set of attributes in another relation.

  引用完整性表示一個關系中的值也必須出現在另一個關系中的一組特定屬性中。

  Modifications in the database could turn out to violate the referential integrity and such actions are rejected by the normal procedure.

  數據庫中的修改可能會違反參照完整性，并且此類操作將被常規過程拒絕。

• Assertions

  斷言

  Assertions are the conditions that are needed to be satisfied by the database. The above two constraints, Domain Constraints and Referential Integrity Constraints are the special forms of assertions.

  斷言是數據庫需要滿足的條件。 以上兩個約束(域約束和引用完整性約束)是斷言的特殊形式。

  System checks for the validity of the assertion and if it does not fit the validity criteria, no further modifications are done to the database.

  系統檢查斷言的有效性，如果不符合有效性標準，則不會對數據庫做進一步的修改。

• Authorization simply means to provide access or permission to the differentiated users on various data values in the database.

  授權只是意味著對數據庫中的各種數據值向有區別的用戶提供訪問或許可。

  Most common authorizations are:

  最常見的授權是：

• Read Authorization – It only allows the user to read the data.讀取授權 –僅允許用戶讀取數據。
• Insert Authorization – It only allows the user to insert the data.插入授權 –僅允許用戶插入數據。
• Update Authorization – It only allows the user to modify the data.更新授權 –僅允許用戶修改數據。
• Delete Authorization – It only allows the user to delete the data.刪除授權 –僅允許用戶刪除數據。

DDL acts like any other programming language, in which an input is taken by the user and the output is generated. These outputs are further stored in the Data Dictionary.

DDL與任何其他編程語言一樣，由用戶接受輸入并生成輸出。 這些輸出進一步存儲在數據字典中。

2)數據處理語言 (2) Data-Manipulation Language)

Data Manipulation Language (DML) is a language that provides the facility to access or manipulate the data to the user. There is various type of access, such as, retrieval, insertion, modification, and deletion of the information that is stored in the database.

數據操作語言(DML)是一種語言，它提供了訪問或操作用戶數據的工具。 有各種類型的訪問，例如，對數據庫中存儲的信息的檢索，插入，修改和刪除 。

DML are further classified into two types:

DML進一步分為兩種類型：

• Procedural DMLs

  程序DML

  It is required from the user to specify what type of data is needed and how one can reach up to that data.

  用戶需要指定所需的數據類型以及如何獲取該數據。

• Declarative DMLs

  聲明性DML

  These are also referred to a

  這些也稱為

  Non – Procedural DML that requires from the user only to specify what type of data is needed and it doesn't specify how to reach up to that data.

  非–程序DML ，僅要求用戶指定所需的數據類型，而未指定如何獲取該數據。

  Declarative DMLs are easy to learn and use than Procedural DMLs.

  聲明性DML比過程DML更易于學習和使用。

  But in

  但在

  Declarative DMLs when the user doesn’t specify how to reach up to that data, this is the responsibility of the database system to figure out itself how to do so.

  當用戶不指定如何到達該數據時，使用聲明式DML ，這是數據庫系統自行確定如何做到的。

The query is a statement that requests for the retrieval of the information. Query Language is the portion of the DML that involves information retrieval. Therefore, Query Language and Data Manipulation Language, these terms are used synonymously, although they are technically incorrect.

該查詢是請求檢索信息的語句。 查詢語言是DML中涉及信息檢索的部分。 因此，“ 查詢語言”和“ 數據操作語言”在技??術上不正確，但它們是同義詞。

3)數據控制語言 (3) Data Control Language)

Data Control Language provides the facility of the authorization in the database. All the commands used in DDL and DML can further be authorized with DCL.

數據控制語言提供了數據庫中授權的便利。 DDL和DML中使用的所有命令都可以進一步通過DCL授權。

The drawback of DCL is that one cannot rollback the command as DCL allows only implicit commit. This mainly occurs in Oracle Database. Some of the commands of DCL are:

DCL的缺點是無法回滾該命令，因為DCL僅允許隱式提交。 這主要發生在Oracle數據庫中。 DCL的一些命令是：

Grant: It allows only specific user to perform specific tasks.

授予：僅允許特定用戶執行特定任務。

Revoke: It allows the cancellation of the previously granted permissions or the denied one.

吊銷：它允許取消先前授予的權限或被拒絕的權限。

4)交易控制語言 (4) Transaction Control Language)

Transaction Control Language is used to manage the transactions in the database. The functions performed by DML are further managed by this language. It allows the statements to be grouped together into logical transactions. TCL performs the following tasks:

事務控制語言用于管理數據庫中的事務。 DML執行的功能由該語言進一步管理。 它允許將語句組合在一起成為邏輯事務。 TCL執行以下任務：

Commit: It is used to save the transaction in the database.

提交：用于將事務保存在數據庫中。

Rollback: It is used to restore the database to the last committed state.

回滾：用于將數據庫還原到最后的提交狀態。

Savepoint: It is used to store the transaction temporarily such that one can easily rollback to the transaction when needed.

保存點：用于臨時存儲事務，以便在需要時可以輕松回滾到該事務。

翻譯自: https://www.includehelp.com/dbms/database-languages-in-dbms.aspx

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